Fig 1.
Prosthetic feet with stiff forefoot keel structures should conform to more consistent roll-over shapes when walking with added loads compared to feet with compliant forefoot keel structures.
Compliant prosthetic feet (red, middle) will continue to bend when users carry their body weight (BW) plus added loads (AL). This continued bending should lead to a roll-over shape with a smaller radius. Stiff prosthetic feet (blue, right) should have only a slight amount of additional bending when users carry added loads. KABW = forefoot stiffness at loads above body weight.
Fig 2.
Load versus deflection profiles for each foot were obtained using a servohydraulic universal test frame (MTS 858, MTS, Eden Prairie, MN) with axial/torsional capabilities, a computer-based data acquisition system (Wintest, Bose, Framingham, MA), and a load cell (MTS 661-21A-01, MTS, Eden Prairie, MN).
The load frame applied uniaxial loads to the foot.
Fig 3.
Marker placement for roll-over shape characterization.
Subjects wore a 22-kg vest for all weighted walking conditions (left). Center of pressure data were transformed into an anatomically relevant socket coordinate system (right) in order to calculate roll-over shapes for each prosthetic ankle-foot system under investigation.
Table 1.
Subject demographics.
Fig 4.
Load versus displacement curves from the ninth loading cycle obtained during mechanical characterization.
The horizontal line represents body weight. Maximum load represents body weight plus the weighted vest (22 kg). Small discontinuities evident in some curves (e.g., near the maximum load of Subject A using the Soleus) represent momentary sticking at the loading interface despite the low-friction PTFE sheet affixed to the boot tread.
Fig 5.
Mean (± 1 standard deviation) forefoot stiffness at loads above body weight (KABW).
Results are sorted from least (left) to greatest (right) forefoot stiffness.
Fig 6.
Roll-over shapes from all trials of the All Pro and Thrive during weighted and unweighted walking for Subject A.
Roll-over shapes are shown in a socket-based coordinate system with the origin at the knee center.
Fig 7.
Mean (± 1 standard deviation) roll-over shape radii (normalized by height) across all subjects.
Results are sorted from smallest (left) to largest (right) mean unweighted roll-over shape radius for each foot.
Fig 8.
Mean (± 1 standard deviation) change in roll-over shape radius (unweighted—weighted) across all subjects.
Results are sorted from the smallest (left) to largest (right) difference in roll-over shape radii (normalized by height).
Fig 9.
Mean (± 1 standard deviation) change in effective foot length ratio (unweighted—weighted) across all subjects.
The effective foot length ratio is a fraction of the total foot length that is effectively used during the single-support phase of gait. Results are sorted from the smallest (left) to largest (right) difference in effective foot length ratio.
Fig 10.
Mean (± 1 standard deviation) late-stance energy return across all subjects sorted from the least (left) to most (right) unweighted energy return.